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21.
22.
本文利用中心流面法的概念,指出叶轮机械的设计白变数在内、外环壁面上应有附加的限制条件,并导得其具体简明方程。同时,还定性地分析了S1流面的翘曲情况。 相似文献
23.
D. Niarchos P.J. Viccaro G.K. Shenoy B.D. Dunlap J.K. Yakinthos 《Journal of Physics and Chemistry of Solids》1983,44(4):307-309
The values of the magnetic moments and the electric field gradient in TmNi3 and TmCo3 are obtained from 169Tm Mössbauer spectroscopy. These values are compared to those from crystal field model based on point charge calculations for these intermetallics. 相似文献
24.
本文求出了Eliashberg方程在T=Tc时的解,得到了下面的临界温度级数表示式: 其中α0(μ*),α1(μ*)等系数是μ*的函数.此式表明,Tc不仅依赖于λ,〈ω2〉和μ*,而且依赖于有效声子谱α2F(ω)的各级矩〈ω2n〉.这是区别于前人的Tc公式最重要的一点。这说明像McMillan以及Allen和Dynes的Tc公式不仅是近似的,而主要是他们没有能正确地概括出α2F(ω)对Tc的影响. 相似文献
25.
R.L. Rasera G.K. Shenoy B.D. Dunlap D.G. Westlake 《Journal of Physics and Chemistry of Solids》1979,40(1):75-77
Time-differential perturbed γ-ray angular correlation experiments have been carried out on 181Ta impurities in ?-phase zirconium hydride over the temperature range from 20 to 588 K. A static, slightly asymmetric electric quadripole interaction is found at all temperatures. The static nature of the pattern indicates the absence of significant hydrogen diffusion at these temperatures on the time scale of the experiment (0.1 μsec). The temperature dependence of the static quadrupole frequency is given by the relation vq(t) = 130[1 ? (1.9 × 10?5)T1.5] MHz. 相似文献
26.
用分子动力学方法和不同参数的指数 6势函数计算了T =30 4K的高密度氦的等温压缩线和能量分布 .给出了能精确描述高密度氦原子间相互作用的指数 6势函数优化参数 .并用优化的势函数计算了高密度氦T =30 0K和T =2 98K的等温压缩线 ,计算结果和实验值非常吻合 .进一步用优化的势函数模拟了高温高密度氦的状态方程及其结构 ,发现当把 ρ限定为 1 .6 0g /cm3 时 ,其径向分布函数的第 2个峰将在 2 0 0 0~ 30 40K区间消失 ,表明此时发生了固 液相变过程 . 相似文献
27.
Part I. Chromatography using ultra-stable metal oxide-based stationary phases for HPLC 总被引:1,自引:0,他引:1
The first part of the review contrasts the main drawbacks of silica-based packings such as their relative thermal and chemical instability with excellent stability of metal oxides. The paper concerns mainly ZrO2, TiO2 and Al2O3. Methods of preparation of spherical particles for HPLC are described. Surface chemistry of the oxides is, however, very different from that of silica. Ability of the oxides to ion- and ligand exchange is discussed from a chromatographic point of view. 相似文献
28.
29.
Alloys of the composition Al98Fe2 have been prepared by rapid quenching from the melt and mechanical alloying methods and have been studied by Xray diffraction techniques and room temperature 57Fe Mössbauer effect methods. Results may be summarized as follows: The rapidly quenched sample is a single phase supersaturated fcc Al–Fe alloy. Mössbauer effect spectra indicate the presence of a substantially greater degree of Fe clustering than is expected for a random distribution of atoms on the lattice sites. Mechanically alloyed samples have been studied as a function of milling time and show the initial formation of a supersaturated fcc phase with microstructural properties which are quite similar to those of the rapidly quenched sample. Further milling results in the reduction of the average grain size and the formation of an amorphous phase. Mössbauer studies and previously reported phase diagrams suggest that a substantial fraction of the Fe resides in this phase. 相似文献
30.
Jordan DB Li XL Dunlap CA Whitehead TR Cotta MA 《Applied biochemistry and biotechnology》2007,141(1):51-76
β-d-Xylosidase from Selenomonas ruminantium is revealed as the best catalyst known (k
cat, k
cat/K
m) for promoting hydrolysis of 1,4-β-d-xylooligosaccharides. 1H nuclear magnetic resonance experiments indicate the family 43 glycoside hydrolase acts through an inversion mechanism on
substrates 4-nitrophenyl-β-d-xylopyranoside (4NPX) and 1,4-β-d-xylobiose (X2). Progress curves of 4-nitrophenyl-β-d-xylobioside, xylotetraose and xylohexaose reactions indicate that one residue from the nonreducing end of substrate is cleaved
per catalytic cycle without processivity. Values of k
cat and k
cat/K
m decrease for xylooligosaccharides longer than X2, illustrating the importance to catalysis of subsites −1 and +1 and the
lack there of subsite +2. Homology models of the enzyme active site with docked substrates show that subsites bey ond−1 are
blocked by protein and subsites bey ond +1 are not formed; they suggest that D14 and E186 serve catalysis as general base
and general acid, respectively. Individual mutations, D14A and E186A, erode k
cat and k
cat/K
m by <103 and to asimilar extent for substrates 4NPX and 4-nitrophenyl-α-l-arabinofuranoside (4NPA), indicating that the two substrates share the same active site. With 4NPX and 4NPA, pH governs k
cat/K
m with pK
a values of 5.0 and 7.0 assigned to D14 and E186, respectively. k
cat (4NPX) has a pK
a value of 7.0 and k
cat (4NPA) is pH independent above pH 4.0, suggesting that the catalytically inactive, “dianionic” enzyme form (D14-E187-) binds
4NPX but not 4NPA.
The mention of firm names or trade products does not imply that they are end orsed or recommended by the US Department of
Agriculture over other firms or similar products not mentioned. 相似文献